Other



atent fiice 2,899,393 Patented Aug. 11, 1959 ELECTROLYTE CONTAINING A KETONE, AN l:ALKALINE: EARTH METAL IODIDE, AND

ODINE l John F. Schoeppel, Stuart L; Varner, and Frederick W.

HernGrand Rapids, Mich., assignors to Lear, Incorporated, Grand Rapids; Mich, a corporation of 1111- nois N Drawing. ApplicationSeptember 6, 1956 Serial No. 608,178

9' Claims. (CL- 252--62.2)

This invention relates to improvements in variable resistors of the types which'comprise a. closed receptacle containingra liquid electrolyte. and'electrodes having a surface adaptedto. contact said electrolyte and to provide aacurrent-conductingpath: between said electrolyte and said electrodes. Such 'variable resistors include, but are not limited to; devices :of the types shown in US. Patents Nos. 2,367,465; 2,376,377; and 2,387,313, sometimes referred to. as liquid levell'switc h'es. In this latter type ofdevice, an. air bubblexwithin the aforesaid closed receptacle. shifts about, upon tilting of the switch, to expose more -or.- lesssof the electrode surface or surfaces whereby current through electrical circuits isvaried. These and simil'ardevices findsuse-fora variety of purposes as, forv example, in..aircraft 'instrumentsfor controllingethe erection-ofivertical gyroscopes. The present invention iss'not concerned with any specific constructions of variable resistors. Rather, it relates to variable resistors'of, the-broad: typedescribed in which, by reason of the utilization therein of the electrolytes hereafter described -in detail, marked. improvements in the operation and usefulnessof said variable resistors is-obtained.

A' fully satisfactory. electrolyte for use in variable resistors ofthe typehere involved must satisfy a number ofrigid and exacting criteria. Not only must it have good conductivity over a Wide rangeof temperatures both above and below 0 degrees C. but it must also have long life and-stability under.thevariousconditions under which it is used. In addition, it must possess the characteristics ofproviding' a. nearly completely reversible reaction, it must not become too viscous under conditions of low temperature, it must be substantially inert to the electrodes and other materials withwhich vit comes into contact, and it must not exhibit .material physical instability due to thermaldeffects in'the variable resistor. These and otherdesirablev characteristics for. a fully satisfactory variable resistor electrolyte have been appreciated by others but, so far, although various compositions have been suggested by others andxused, there has been much left to be desired in the achievement of an ideal electrolyte.

The electrolytes which are used in accordance with the present. invention represent a distinct improvement in at least most of the characteristics which are desired in such products over anything which, so far as is known, have heretofore been suggested or utilized. In general, the electrolytes comprise solutions, in ketones, of certain iodides, hereafter disclosed, and iodine, The ketones can be chosen from the aromatic, aromatic-aliphatic, aromaticcycloaliphatic, cycloaliphatic, and aliphatic groups, it being particularly desirable to utilize the aliphatic ketones. Illustrative examples of such ketones are benzyl ketone, naphthyl ketone, benzyl ethyl ketone, cyclohexyl benzyl ketone, cyclohexyl isopropyl ketone, methyl isobutyl ketone, methyl amyl ketone, methyl ethyl ketone, diethyl ketone, methyl n-propyl ketone, n-amyl ketone, n-hexyl ketone,-n-heptyl ketone, diisopropylketone, diisobutylketone; and the like; as well as mixtures of anytwo or more thereof. Of particularutilit-y are diisopropylketone and diisobutylketone and preferably mixtures thereof in which the ratio thereof, by volume, is fromtabout l to-3 to about 3 to 1 and, more especially, from about 2 to 3 to about 3 to 2.

The iodides which are utilized in accordance with the present invention comprise those of calcium, magnesium, strontiumandbarium; namely, the alkaline earthmetal iodides, and compatible mixtures thereof;

The proportions of the ingredients of the electrolyte can be varied, within reasonable limits, dependingupon the particular results desired. In all cases; of course,- the electrolyte is in liquid form and comprises a solution, in a ketone or mixture of ketones, of the aforesaid iodide or iodides and iodine. In general, in each ml. of electrolyte solution there should be present from about 3 to about 10 grams of said iodide and from about 8 to about 16 grams of iodine. A particularly preferred range .of proportions comprisesfrom about 4 to about 6*gramsof said iodide and from about 10 to about 14 "grams-of iodine in each 100' of electrolyte solution. It will be understood that, in general, an increase in the concentration of the said iodide will, up to a-certain point depending upon its solubility in the particular ketone or mixture of .ketones utilized and depending upon the concentrationtof iodine, result in an increase in electrical conductivity of theelectrolyte solution. However, the concentrationof the said iodide should not be increased beyond the point where the stability of'the variable resistor is affected and Where, at low temperatures under which the variable resistor may be required to function, the saidiodide may crystallize orseparate out of the electrolyte solution- In the case of the iodine, an increase in its concentration up to a certain point will, in general, increase the conductivity of the electrolyte solution. Beyond that point, a further increase in the iodine concentration. tends, in general, to have little eilect at room temperatures and,in: at least certain cases, the electrical conductivity is decreased at low temperatures as, for example, temperatures of the order of -50 to 55 degreesC. The ratio of the said iodide to iodine in the electrolyte solution is quite variable. Excellent results, for example, are obtained with ratios of 1 to 6and even higher. While, in general, and in the particularly preferred embodiments of the invention, the iodine is advantageously present in amount greater than the amount of said iodide, the invention is not so limited. Satisfactory results can be obtained with the use of elec trolytes in which the ketone solution contains b'oth 'iodine and said iodide and wherein the iodine is present 1 in amount less than the amount of said iodide as, for instance, With ratios of 1 of iodine to l to 2 of said iodide.

The following examples are illustrative of electrolytes the use of-whichis variable resistors falls within the scope of the invention.- It will beunderstood that such examples are in no way limitative of the invention since-numerous other electrolyte compositions can readily be prepared in the light Olf the guiding principlesand teachings disclosed herein. Thus, for example, other ketones and mixtures of various ketones can be utilized, and the proportions of-the ingredients can be varied, within reasonable limits, as desired. The stated quantities of the aforesaid iodide and iodine represent the number of grams of each inrl00 'ml. of the electrolyte solution made by dissolving the said iodide and the iodine in the stated ketone or mixture of ketones.

3 Example 2 Methyl n-propyl ketone.

Magnesium iodide Iodine 11 Example 3 Diisopropylketone.

Strontium iodide 4 Iodine 7 Example 4 Diisobutylketone.

Barium iodide 5 Iodine 9 Example 5 ggzgg gfgggg equal parts by volume. Strontium iodide 4 Calcium iodide 3 Iodine Example 6 32285535535553? equal parts by volume. Magnesium iodide 5 Iodine 9 Example 7 ggzggf gfigggg equal parts by volume. Calcium iodide 5 Magnesium iodide 2 Iodine 11 Example 8 Methyl ethyl ketone.

Strontium iodide 6 Iodine 6 Example 9 Methyl isobutyl ketone.

Barium iodide 6 Iodine 5 Example 10 Methyl n-propyl ketone.

Calcium iodide 7 Iodine 6 Example 11 Diisobutylketone.

Strontium iodide 4 Calcium iodide 3 Iodine 7 Example 12 Diisopropylketone.

Barium iodide 5 Iodine 7 For best results, certain precautions should be exercised in carrying out the preparation of the electrolyte solution. The iodide should be CF. and anhydrous and the iodine should be 0.1. and resublimed. The ketone may be pure or of practical grade. The materials should be so handled as to insure against contamination and to protect the same against moisture. To these ends, the iodide and the iodine should be stored, prior to use, in closed containers in a desiccator or the like and, when handled, as for weighing or the like, should be placed on glass or the like to avoid any possible metallic contamination. The finished liquid electrolyte, Where stored, should be kept in sealed glass or the like containers and, if the latter are stored in air, it is advantageous that the dew point of the air does not exceed about 55 degrees F. To facilitate the maintenance of the precautions described above, it is, in general, advisable to work with small batches of the materials.

In preparing the electrolyte solutions, a good operating technique comprises, for example, in an illustrative case, placing 2.5 grams of calcium iodide in an open, small mouth container of about 60 ml. capacity which previously has been cleaned and dried and which can easily be sealed. The container and its contents of calcium iodide is then placed in a vacuum heating chamber and evacuated to about 25 inches of mercury and heated to approximately 150 degrees F. for about 30 minutes. Promptly upon removal of the container from the vacuum chamber, 6 grams of iodine crystals are placed in said container, and then 25 ml. of diisopropylketone and 25 ml, of diisobutylketone are added to the container and the ingredients are thoroughly mixed to efifect solution of the calcium iodide and iodine. The container is then sealed until the electrolyte solution is ready to be used.

In use, the interior of the resistor casing into which the electrolyte is introduced is thoroughly washed with a ketone, for example, diisobutylketone, using several rinses. The devices are placed in a vacuum heating chamber, evacuated to about 25 inches of mercury, and heated to about 150 degrees F. for about 30 minutes. The device is placed in a suitable leveling fixture and the liquid electrolyte is introduced into the device to the desired level by means of a hypodermic syringe or the like and the casing is then closed. The usual techniques in filling, sealing and testing the finished devices are employed.

While the invention has been described in detail, it will be understood that various modifications may be made without departing from the essential teachings set forth herein and which are delineated in the appended claims.

What is claimed as new and desired to be protected by Letters Patent of the United States is:

1. In a variable resistor which includes a closed receptacle containing an electrolyte and electrodes having a surface adapted to contact said electrolyte to provide a current-conducting path between said electrolyte and said electrodes, the improvement wherein said electrolyte is a solution, in a saturated ketone, of iodine and an alkaline earth metal iodide, wherein said alkaline earth metal iodide is present in proportions ranging from about 3 to about 10 grams per m1. of said electrolyte solution, and the iodine is present in proportions ranging from about 8 to about 16 grams per 100 ml. of said electrolyte solution.

2. A variable resistor in accordance with claim 1, wherein said ketone is an aliphatic ketone.

3. In a variable resistor which includes a closed receptacle containing an electrolyte and electrodes having a surface adapted to contact said electrolyte to provide a current-conducting path between said electrolyte and said electrodes, the improvement wherein said electrolyte is a solution, in a saturated ketone, of calcium iodide and iodine, the calcium iodide being present in proportions ranging from about 4 to about 6 grams per 100 ml. of said electrolyte solution, and said iodine being present in proportions ranging from about 10 to about 14 grams per 100 ml. of said electrolyte solution.

4. A variable resistor in accordance with claim 1, wherein said ketone comprises at least one member selected from the group consisting of diisopropylketone and diisobutylketone.

5. A variable resistor in accordance with claim 1, wherein said ketone comprises a mixture of diisopropylketone and diisobutylketone in which the ratio of said ketones to each other by volume is from about 1 to 3 to about 3 to 1.

6. A variable resistor in accordance with claim 1, in which said ketone is a mixture of diisopropylketone and diisobutylketone and in which the ingredients of said electrolyte are present in the following amounts relative to 9. A variable resistor in accordance with claim 2, each other: wherein said iodide comprises strontium iodide.

Diisopropylketone Il'll 5O Diisobutylketone m] 50 References Cited in the file of this patent Alkaline earth metal iodide grams 5 5 UNITED STATES PATENTS Idme 12 2,387,313 Wilson Oct. 23, 1945 7. A variable resistor in accordance with claim 2, 53 schoeppel Sept. 25, 1956 wherein said iodide comprises magnesium iodide.

OTHER REFERENCES 8. A variable resistor in accordance with claim 2, 10 wherein said iodide comprises barium iodide. Chem. Abstracts 47, 1953, p. 27. 

1. IN A VARIABLE RESISTOR WHICH INCLUDES A CLOSE RECEPTACLE CONTAINING AN ELECTROLYTE AND ELECTRODES HAVING A SURFACE ADAPTED TO CONTACT SAID ELECTROLYTE TO PROVIDE A CURRENT-CONDUCTING PATH BETWEN SAID ELECTOLYTE AND SAID ELECTRODES, THE IMPROVEMENT WHEREIN SAID ELECTROLYTE IS A SOLUTION, IN A SATURATED KETONE, OF IODINE AND AN ALKALINE EARTH METAL IODINE, WHEREIN SAID ALKALINE EARTH METAL IODINE IS PRESENT IN PROPORTIONS RANGING FROM ABOUT 3 TO ABOUT 10 GRAMS PER 100 ML. OF SAID ELECTROLYTE SOLUTION AND THE IODINE IS PRESENT IN PROPORTIONS RANGING FROM ABOUT 8 TO ABOUT 16 GRAMS PER 100 ML. OF SAID ELECTROLYTE SOLUTION. 